Voltage Sensitivity on a Multimeter
Sensitivity is a technical indicator that indicates the degree to which the instrument responds to weak energy.
Since the energy for driving the deflection of the measuring mechanism of the instrument is taken from the current in the circuit under test, if the pointer of the instrument is deflected by a large amount and uses a small amount of energy, its sensitivity will be higher.
The sensitivity of the multimeter can be divided into three indicators: DC voltage sensitivity, AC voltage sensitivity and meter sensitivity. The DC voltage sensitivity is the main indicator. AC voltage sensitivity is generally lower than DC voltage sensitivity due to meter circuit design factors. They are marked on the dial in ohms per volt (Ω/V).
The sensitivity of the meter head indicates the full-scale current value of the meter head, and also includes two indicators, the internal resistance and linearity of the meter head, which are the basis for calculating the meter circuit, and also determine the voltage sensitivity of the entire multimeter; the internal resistance of the meter head refers to the pointer of the meter. The sum of the resistance values of the moving coil and the upper and lower hairsprings; linearity refers to the degree of consistency between the current intensity passing through the meter and the deflection amplitude of the needle, which is used as the basis for the scale drawing of the dial. The focus here is on the DC voltage sensitivity of the multimeter.
When the voltmeter is used for measurement, it is connected in parallel with the two points under test. Due to the existence of the internal resistance of the voltmeter, it is equivalent to connecting a resistor in parallel between the two points under test, which reduces the total impedance between the two points under test; Coupled with its shunting effect on the circuit, the measured voltage value is lower than the actual value. Therefore, when doing voltage measurement, the multimeter is required to have a large internal resistance (that is, the sensitivity Ω/V number should be high) to reduce this error.
For example, the DC voltage range of the MF30 multimeter is 0-1-5-25-100-500V, and the dial is marked with 20000Ω/V, then the internal resistance of the 1V range is 20kΩxl=20kΩ; the internal resistance of the 5V range is 20kΩx5=100kΩ , and so on.
